Isocyanates in marine sponges: Axisocyanate-3, a new sesquiterpene from Acanthella cavernosa

Pinus Jumaryatno,Mary J Garson,Joanne T Blanchfield,Karen Rands-Trevor,Paul Krapcho

doi:10.3998/ark.5550190.0008.713

Abstract

The isolation of axisocyanate-3 as a minor component of Acanthella cavernosa has been confirmed by spectroscopic characterisation of the metabolite, and by conversion of a mixture of axisothiocyanate-3 and axisocyanate-3 to their diethyl(thio)urea derivatives. The role of isocyanates in the formation of urea metabolites in sponges has been investigated through a model study with a menthyl-derived isocyanate.

Highlights

Bioactive terpenes functionalized by the presence of isocyano, isothiocyanato and formamide groups are a common structural motif in marine sponge chemistry
We report the isolation of a new isocyanate with a spiroaxane skeleton from the well-known Indo-Pacific sponge Acanthella cavernosa, and describe a biomimetic reaction with menthyl isocyanate that may illustrate the role of terpene isocyanates in the formation of sponge natural products
Isocyanate metabolites are labile metabolites in marine sponges whose presence may frequently have gone undetected in isolation work owing to their sensitivity to hydrolytic conditions

Summary

Introduction

Bioactive terpenes functionalized by the presence of isocyano, isothiocyanato and formamide groups are a common structural motif in marine sponge chemistry. Much less commonly encountered are terpenes functionalized by thiocyanato, dichloroimine or isocyanato functional groups.[1,2] Examples of the isocyanate functionality in the marine terpene literature include the bisabolene (1)[3] and aromadendrane (2)[4] sesquiterpenes, the amphilectane diterpenes 3-5,5,6 and the kalihinol A derivative 6.7 Novel biological activites have been described for these metabolites; compounds 3-5 are cytotoxic with 5 showing potent and selective antiplasmodial activity,[8] while 6 inhibits the metamorphosis of barnacle larvae.[7] In contrast, isocyanate 2 is non toxic to fish and has been proposed to play a role in the detoxification of isocyano metabolites in Acanthella cavernosa.[4] The recent reports of symmetrical sesquiterpenes containing urea functionality in marine sponges[9,10,11] hint at a possible role of isocyanates in their biosynthesis, and suggest that isocyanate metabolites might occur more widely in marine sponges than has been reported. We report the isolation of a new isocyanate with a spiroaxane skeleton from the well-known Indo-Pacific sponge Acanthella cavernosa, and describe a biomimetic reaction with menthyl isocyanate that may illustrate the role of terpene isocyanates in the formation of sponge natural products

Findings

Result and Discussion

Conclusion